Electric discharge tube



y 20, 1958 H. A. WKTTEVEEN ELECTRIC DISCHARGE TUBE Filed March 18, 1952INVENTOR Her-mun Adam WiHex/een United States PatentO ELECTRIC DISCHARGETUBE Herman Adam Witteveen, Eindhoven, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc.,New York, N. Y., a corporation of Delaware Application March 18, 1952,Serial No. 277,103 Claims priority, application Netherlands April 13,1951 2 Claims. (Cl. 313-239) This invention relates to an electricdischarge tube. In particular, the invention relates to an electricdischarge tube comprising a cathode which evaporates a conductingmaterial and a plurality of connector pins sealed on a circular arc in aportion of the tube housing.

Tubes of the foregoing type, particularly small tubes, have adisadvantage in that metal evaporating from the cathode settles on thewall portion of the housing containing the connector pins to form asemi-conducting coating. This results in leakage current paths betweenthe individual pins which impairs the operating characteristics of thetube.

It is an object of the invention to provide a novel construction for atube of the foregoing type which avoids the disadvantages resulting fromthese leakage paths.

This and other objects of the invention will be best understood from thefollowing description.

According to the invention, in an electric discharge tube having acathode which evaporates a conducting or semi-conducting material and aplurality of connector pins sealed on a circular arc in a wall portionof a housing enclosing the tube, at least one insulating strip issupported by two substantially diametrically-opposed connector pins tooverlie the inner surface of the wall portion containing the pins. Theinsulating strip prevents the evaporated conducting material fromforming a conducting layer on a portion of the surface of the wallportion containing the connector pins lying under the strip and,consequently, prevents the formation of a continuous leakage pathbetween the pins separated by this non-coated surface portion. Thisarrangement has the advantage that the same size insulating strips maybe employed in all discharge tubes in which the connector pins aresealed on a circular are having the same diameter.

The two connectors pins which support the insulating strip are chosen tohave the characteristics that current leakage between these pins willhave slight effect on the operating characteristics of the tube becausethe evaporated conducting material will coat on the surface of the stripto form a leakage path. Where the discharge tube has a large number ofconnector pins, additional strips are provided to assure that thevarious pins are suitably insulated from each other.

The invention will now be described with reference to the accompanyingdrawings wherein:

Fig. 1 is a view, in cross-section, of one form of electric dischargetube in accodance with the invention;

Fig. 2 is a transverse sectional view of the tube shown in Fig. 1 on aplane above strip 14;

Fig. 3 is a view similar to Fig. 2 of another form of electric dischargetube according to the invention;

Fig. 4 is a view similar to Fig. 2 of still another form of electricdischarge tube according to the invention;

Fig. 5 is a view similar to Fig. 2 of still another form of electricdischarge tube according to the invention.

Referring to Fig. 1, an electric discharge tube comprises a housingsealed to a bottom wall portion 11. The housing 10' encloses anelectrode assembly 12 ineluding a cathode 13 which evaporates aconducting material during operation and one or more other electrodessuch as 16 which is connected to base pin 3. A plurality of connectorpins 1 to 8 are arranged on a circular arc and sealed in the bottom wallportion 11 of the tube to provide external circuit connections for thevarious electrodes of the electrode assembly 12. Two insulating strips14-, 15 are provided to prevent leakage between the various connectorpins 1 to 8 resulting from metal vapor escaping from the lower end ofthe cathode 13 to form a semi-condutive coating on the bottom portion11.

Referring to Fig. 2 which shows the connector pin arrangement for acombination diode-triode tube in one housing, the upper strip 14, whichis preferably of mica, is arranged on two diametrically opposed pins 2and 6 which are connected to the filament and the screen the filamentpins, but such leakage will not impair the operating characteristics ofthe tube.

Furthermore, the leakage current will be small because the pins 2 and 6are remote from. each other and because the very thin metal depositsgenerally have a high resistance.

Metal vapour does not deposit under the strip 14 and a portion of thebottom 11, consequently, remains entirely free from a conductingcoating. Accordingly, the pins 1, 7 and 8 are satisfactorily insulatedfrom the pins 2, 3, 4, 5 and 6. A second strip 15 may be arranged understrip 14 in order that leakage between the said pins may also beavoided. Since the strip 35 is covered in part by strip 14, a continuousleakage path is prevented from being formed across the surface. Even ifthe strips 14 and 15 lie in contact with one another, the sides of strip14 ensures sufficiently satisfactory insulation since a deposit is notformed on these sides, which, in case of mica, are very rough. Byplacing two strips each on dilferent diametrically opposed pins, it isensured that all the pins, except the pins 2 and 6, are satisfactorilyinsulated from each other in spite of the small relative spacing and thepossibility that metal vapour may deposit on the bottom. Since the pinsare located on the circumference of a circle, all the strips may beperfectly equal for any tube type having a bottom with which thediameter of the pin circle is identical.

Fig. 3 shows the invention being employed with the pin connections of acombination triode-hexode tube. In this case, one insulating strip isconnected between pin 5 (hexode screen grids) and pin 1 (commonfilament), while the other strip is connected between pin 7 (commoncathode) and pin 3 (triode anode).

The remaining pin connections are as follows: Pin 2 is connected to thehexode; pin 4 is connected to the triode grid and the third hexode grid;pin 6 is connected to the first hexode grid; pin 8-is connected to thefilament.

Fig. 4 shows the pin connections for a miniature (7 pin base)diode-pentode in which one insulating strip is connected between thefilament (f) and the screen grid (3 p The remaining pin connections areas follows: Kg is the pentode cathode and suppressor grid pin; d is thediode anode; g is the pentode control grid; a is the pentode anode; f isthe common filament.

Fig. 5 shows the pin connections for a double pentode having 9 pins inwhich one strip is connected between the screen grids 3, 7 of eachpentode unit. Although in this case the pins are not exactlydiametrical, the strip still has the same length.

The remaining pin connections are as follows: pins 1 and 9 are thecommon filament; pins 2 and 8 are the anodes for each pentode unit; pins4 and 6 are the control grid for each unit; pin 5 is the common cathodeand suppressor grid connection.

In each of the above-described cases, the strip closest to the cathodeis connected between a pair of pins having the characteristics thatleakage current between them will have only a slight effect on theoperation of the tube.

While we have thus described our invention with specir'ic examples andembodiments thereof, other modifications are readily apparent to thoseskilled in the art without departing from the spirit and the scope ofthe invention as defined in the appended claims.

What I claim is:

1. An electric discharge tube comprising an electrode assembly includinga cathode which evaporates a con ductive material and at least one otherelectrode, a housing enclosing said electrode assembly and including asubstantially flat base portion, a plurality of connector pins arrangedin a circular are on and sealedin said base portion and connected tosaid cathode and said other electrode, respectively, to provide externalcircuit connections therefor, and at least two solid insulatedstrip-like members each supported by a different pair of substantiallydiametrically-opposed connector pins between said base portion and saidelectrode assembly and 4 overlying each other and the inner surface ofsaid base portion to prevent leakage current between said connectorpins, the strip-like member remote from the inner surface of said baseportion being supported by two pins between which leakage current hasonly a slight effect on the operation of the tube.

2. An electric discharge tube as set forth in claim 1 in which thestrip-like members are constituted of mica and extend approximately atright angles to one another.

References Cited in the file of this patent UNITED STATES PATENTS D.135,792 Eitel et a1. June 8, 1943 1,639,805 McCullough Aug. 23, 19271,814,711 Kingdom July 14, 1931 2,087,327 McNally July 20, 19372,112,124 Teves Mar. 22, 1938 2,184,709 Bruijnes et al. Dec. 26, 19392,227,093 Laico Dec. 31, 1940 2,346,913 Depew Apr. 18, 1944 FOREIGNPATENTS 424,111 Great Britain Feb. 14, 1935 U. S. DEPARTMENT OF COMMERCEPATENT OFFICE C ERTIFIC ATE 0F C ORREC TION Herman Adam Witteveen s .inthe printed specification tion and that the said Letters Patent No.2,835,842 May 20, 1958 Column 1, line 4% for "comets-tors" read econnector line 61, for 'aceodence read me accordance g column 2 line 54,after 'he' xode and before the semi=colon insert ed anode e u Signed andsealed this 29th. day of July 1958.,

(SEAL) Attest:

KARL WINE ROBERT c. WATSON Comnissioner of Patents Attesting Officer

